Why does minus and minus equal plus?

Answer 1

Because a minus changes the sign. If you take a plus and change it to a minus,

you get a minus. If you take a minus and change it to a minus, it changes back

into a plus. Because you have only two options, minus and plus, here are all the

options:

• + & - = -
• + & + = +
• - & + = -
• - & - = +

===========================================

Everything above the double line is a misleading, even dangerous

discussion. When it's all over, both the questioner and the responder

think they have it all worked out, where in reality, it's all meaningless.

The main problem is: Neither of them ever explains what ' and ' means

in the question, or what ' & ' means in the answer. Neither of those is

a mathematical operation. The statement in the question, and the list

of 4 'rules' in the answer, are correct for some mathematical operations

and either indeterminate or dead wrong for others.

The question says: " ... minus and minus equal plus. "

-- If ' and ' means multiplication or division, then it's a true statement.

-- If ' and ' means subtraction, then it may or may not be true, depending

on the size of the two numbers.

-- If ' and ' means addition, then it's always false.

In the list of 4 items in the answer:

-- If ' & ' means multiplication or division, then all 4 items are correct

(but almost impossible to remember in this form).

-- If ' & ' means addition, then items #1 and #3 are sometimes true and

sometimes false, item #2 is always true, and item #4 is always false.

-- If ' & ' means subtraction, then item #1 is always false, items #2 and #4

are sometimes true and sometimes false, and item #3 is always true.